Chapter 2

Question 1

3 classifications of media

Answer 1

1) physical state - liquid, semisolid, soli
2) chemical composition - defined or complex
3) functional type (purpose)

Question 2

Defined (synthetic) media VS complex media

Answer 2

• defined media: composition is precisely chemically defined; contain pure organic/inorganic compounds; exact formula
• complex media: one or more components is not chemically defined; contains extracts of animals, plants, or yeasts (blood, serum, meat extracts or infusions, milk, year extract, soybean digest, peptone)

Question 3

General-purpose media

Answer 3

grow a broad spectrum of microbes; generally complex

Question 4

Enriched media

Answer 4

contain complex organic substances (blood, serum, etc) or special growth factors for the growth of fastidious microbes

Question 5

Selective media

Answer 5

contains agent(s) that inhibit the growth of a certain microbe or microbes; important for primary isolation of a specific type of microorganism

Question 6

Differential media

Answer 6

allow multiple types of organisms to grow but display visible differences in how they grow (color, shape, gas production, etc)

Question 7

Reducing media

Answer 7

contains a substance that absorbs O2 or slows the penetration of O2 (grow anaerobic bacteria)

Question 8

Transport media

Answer 8

maintain and preserve specimens that have to be held for a period of time before clinical analysis

Question 9

Carbohydrate fermentation media

Answer 9

contains sugars that can be fermented (converted to acids) with a pH indicator to show this reaction

Question 10

Assay media

Answer 10

used by technologists to test the effectiveness of antimicrobial drugs

Question 11

Enumeration media

Answer 11

used to count the numbers of organisms in a sample

Question 12

What are the phases of magnification in light microscopy?

Answer 12

Real image: the initial image of the specimen formed by the objective

Virtual image: formed when the image is projected up through the microscope body to the plane of the eyepiece, the ocular lens forms a second image

Question 13

What is resolution in light microscopy?

Answer 13

The capacity of an optical system to distinguish two adjacent objects or points from one another

Question 14

What does oil immersion do in light microscopy?

Answer 14

uses oil to capture some of the light that would otherwise be lost to scatter, increasing resolution

Question 15

what is the refraction index?

Answer 15

what measures contrasts

the degree of bending that light undergoes as it passes from one medium to another

the higher the difference in the RI, the sharper the contrast registered by the microscope and the eye

Question 16

Bright-field microscope

Answer 16

• most widely used
• forms its image when light is transmitted through the specimen
• specimen absorbs some of this light and the rest is transmitted directly up through the ocular

Question 17

Dark-field microscope

Answer 17

• a “stop” disk is added to a light-field microscope
• the stop blocks all light from entering the objective lens, except peripheral light that is reflected off the sides of the specimen itself
• produces brightly illuminated specimen surrounded by dark field
• used to see living cells that would be distorted by drying/heat of that cannot be stained with usual methods

Question 18

Phase-Contrast microscope

Answer 18

• take advantage of the fact that cell structures differ in density
• devices that transform the subtle changes in light waves passing through the specimen into differences in light intensity
• produces greater internal detail
• useful for observing intracellular structures

Question 19

Fluorescence Microscope

Answer 19

• furnished with a UV radiation source
• the dyes emit visible light when bombarded by short UV rays
• useful in diagnosing infections and pinpointing particular cellular structures

Question 20

Confocal microscope

Answer 20

• uses a laser beam of light to scan various depths in the specimen and deliver a sharp image focusing on just a single plane
• able to capture a highly focused view at any level
• mostly used on fluorescently stained specimens

Question 21

Transmission Electron Microscope (TEM)

Answer 21

• method of choice for viewing the detailed structure of cells and viruses
• produces its image by transmitting electrons through the specimen
• specimen must be sectioned into extremely thick slices and stained or coated with metals that will increase image contrast

Question 22

Scanning Electron Microscope (SEM)

Answer 22

• provides dramatic and realistic images
• bombards the surface of a metal-coated specimen with electrons
• a shower of electrons deflected from the surface and the electron pattern is displayed as an image on a TV screen
• designed to create a detailed 3D view

Question 23

positive stains

Answer 23

dye sticks to the specimen and gives it colour (usually basic bc they are positive and bacteria usually negative)

Question 24

negative stains

Answer 24

does not stick to the specimen, but settles some distance from its outer boundary, forming a silhouette

Question 25

Simple staining VS Differential staining

Answer 25

• Simple stairs: only require a single dye and an uncomplicated procedure
• Differential stains: uses 2 differently coloured dyes (primary dye and counterstain) to distinguish cell types or parts; more complex

Question 26

Sequence of stains used in Gram staining

Answer 26

crystal violet (primary stain)
gram’s iodine (mordant)
an alcohol rinse (decolorizer)
a contrasting counterstain

Question 27

What colours do gram-positive and negative produce?

Answer 27

gram-positive = purple
gram-negative = red

Question 28

Types of differential stains

Answer 28

gram stain, acid-fast stain, endospore stain

Question 29

Types of special stains

Answer 29

capsular stains, flagellar stains